Cathodic arc deposition is a method that has been established for years, which is used for layer deposition on tools and parts and is used to deposit a wide variety of metallic layers as well as metal nitrides, metal carbides, and metal carbon nitrides. In this method, the targets are cathodes of an arc discharging process that is operated at low voltages and high currents and with which the target (cathode) material is vaporized. DC power supplies are used as the simplest and cheapest power supplies for operating arc discharging processes.
It is known that the material vaporized by cathodic arc discharging contains a high percentage of ions. Johnson, “P.C. in Physics of Thin Films,” vol. 14, Academic Press, 1989, pp. 129-199, describes values of between 30% and 100% for these ions, depending on the cathode material and magnitude of the discharge current. This high percentage of ionized vapor is desirable in layer synthesis.
The high degree of ionization turns out to be particularly advantageous in layer synthesis when it is coupled with a negative bias on the substrate and therefore permits one to increase and vary the acceleration and energy of the ions toward the substrate. The layers synthesized in this way have a higher density and it is possible to influence some layer properties such as the stress of the layer and the layer morphology by changing the bias voltage.
Arc vaporization, however, is also known for the fact that depending on the melting point of the vaporized material, it produces more or less droplets, which are basically not desirable. This percentage of droplets is not usually taken into consideration when indicating the degree of ionization of the vaporized material, but can have a considerable influence on the layer quality. It is therefore desirable to reduce the percentage of droplets in the vaporized material by means of a special source magnetic field or additional filters (mechanical and electromagnetic as described in Aksenov, I. I. et al., Soy. J. Plasma Phys. 4(4) (1978) 425) or to reduce the percentage of them by means of other process parameters such as an increased relative gas pressure. Also, the use of higher-melting materials is proposed in order to reduce the number and size of droplets.
The ionized portion of the vaporized material that is observed in arc vaporization can also be used for pretreating substrates. By successively increasing the substrate bias voltage, its bombardment with the vapor ions of the vaporized material and the working gas can be driven to an extent that permits the substrates to be sputtered and/or heated to high temperatures.
Usually, this process step is referred to as metal ion etching, a somewhat imprecise name, since it does not conceptually include the ions produced by the customary or necessary use of a working gas or reactive gas. Generally, however, it is desirable to reduce the percentage of working gas ions (frequently an inert gas such as argon is used) or to eliminate the working gas entirely. One reason for this is that inert gases cannot be incorporated into layers in a stable fashion since they do not bond and furthermore, result in stresses. In general, however, a continuous operation of the arc source without a gas supply (working gas or reactive gas) is not easily possible. If arc sources must be operated without a working gas, for example the ion sources for ion implantation, then they are operated in pulsed fashion, i.e. the source must be continually reignited since the arc only “lives” for a short time if no gas is added. An example of such a method is described in JP 01042574.
A pretreatment of substrates by means of ion bombardment and the associated etching of the substrate by means of ions as well as the heating of the substrate have already been described in U.S. Pat. No. 4,734,178.
It is important to add here that etching by means of metal ions can lead to treatment results on the substrate surface that differ from those achieved with a simple heating of the substrate or also with a heating of the substrate by means of electron bombardment as described, for example, by Sablev in U.S. Ser. No. 05/503,725. Even the mere use of metal ions yields new reaction possibilities by comparison with inert gas ions, for example the formation of carbides or mixed crystals.
Combinations of implantation and diffusion processes are described in the literature, which result in an integration of the metal ions into the substrate surface and therefore a favorable coupling of the subsequently vapor-deposited layer (Muenz, W.-D. et al., Surf. Coat. Technol. 49 (1991) 161, Schonjahn, C. et al., J. Vac. Sci. Technol. A19(4) (2001) 1415).
The problem with this process step, however, is primarily the existence of metallic droplets whose mass is a multiple of the atomic mass and which usually cannot be removed again by means of an etching step if they come into contact with the substrate surface and condense there.
One way to circumvent this situation is to equip the arc sources with filters that separate the droplets from the ions.
A known filter design is based on the work of Aksenov, I. I. et al., Soy. J. Plasma Phys. 4(4) (1978) 425; the arc source is connected to the deposition chamber via a tube that encloses a magnetic field and has a 90° bend. The magnetic field guides the electrons along a curved path and these in turn force the ions, by means of electrical forces, to follow a similar curved path. The uncharged droplets, however, collide with the inner wall of the tube and are thus prevented from reaching the substrate. The resulting reduction in the rate plays a subordinate role for purposes of metal ion etching. It is very disadvantageous, however, that the usable diameter of the ion beam exiting the tube into the deposition chamber has a diameter of only a few centimeters to approximately 10 cm. For many applications, this makes it necessary to move the substrate in front of the source in order to assure sufficient uniformity of the etching process. This excludes these methods from being used for normal batch deposition systems of the type conventionally used for production.
A significantly simpler approach is to work with a baffle plate in front of the arc source and with an offset-positioned anode situated approximately behind the substrate (for example the use of another source as an anode on the opposite side of the chamber) as already been basically outlined in principle in Sablev U.S. Ser. No. 05/503,725, but not described specifically for the MIE process (MIE=metal ion etching). The path of the electrons then passes through the chamber and is forced past the substrates. The electrical fields also force the ions to follow the paths close to the electrons and are thus available for the etching process in the vicinity of the substrate. The droplets are predominantly captured at the baffle plate. This process guidance would be very ineffective for a deposition process because ionized material is also lost at the baffle plate and in the edge regions. However, since in the prior art, the typical processes for metal ion etching require only low currents of a few amperes and etching takes place for only a few minutes, such an operation can in fact be justified for use in production processes. Such an operation, however, which forces the ions onto the electron paths through the substrate holder, requires an anode that is separate from the chamber potential. This requires additional space in the chamber, which in turn reduces the productivity of the system. The above-cited intermittent use of another arc source as an anode has the disadvantage that this source becomes clogged and only becomes usable again if it is cleaned by means of an undesirable “free arcing.”
In summary, it would be desirable in MIE if it were possible to eliminate a baffle plate and it were no longer necessary to operate the arc source by means of a separate anode, but instead, the arc sources could be operated with the substrate chamber functioning as an anode (ground) without producing an excessive amount of droplets, primarily ones of large diameter. In addition, it would be desirable to arrive at zero layer growth on the substrate already at a moderate substrate bias (less than 1500 V, preferably less than 800 V) and to have the possibility, by changing the substrate bias, of shifting from the layer deposition phase into the etching phase and vice versa.
Due to the formation of droplets in the arc method, attempts have been made to produce the ions not by means of an arc source, but by means of a sputter source, as described in EP 01260603. It is known that far fewer droplets are produced with the sputtering process. However, it is also known that conventional sputter sources produce much fewer ions. It has been successfully demonstrated, however, that operating sputter sources by means of pulsed power supplies significantly increases the ion density during the pulse. This “High Power Pulsed Magnetron Sputter Method” (HIPIMS) Ehiasarian, A. P. et al., 45th Annual Technical Conference Proceedings, Society of Vacuum Coaters (2002) 328 appears to be well suited for producing significantly more ions than are produced in normal sputtering methods, primarily even metallic ions as well.
A disadvantage of this method, however, is the fact that a significantly more powerful magnetic field in the target is required in order to ignite a magnetron discharge. This more powerful magnetic field, however, disadvantageously results in the capture of the ions produced in the high-energy pulse so that and only a small portion of them reaches the substrate.
A much greater disadvantage of this method, however, is the incompatibility of the HIPIMS-MIE method with PVD deposition in the sense that most of the time, these sources cannot be used for the actual deposition.
The deposition rates with the HIPIMS method are so low that in most cases, additional sources must be used for a layer deposition and it is not possible to use the HIPIMS sources for a layer deposition. This is inconsistent with increasing the productivity of the production systems. And finally, the sputter method likewise requires an inert gas such as argon as a working gas.
The disadvantages of the previously used metal ion etching methods based on cathodic arc vaporization can be summarized as follows:                1. Depending on the target material, the unfiltered arc sources produce a large amount of droplets, some of which have large diameters. These droplets do not have enough energy to permit them to completely react chemically with the components of the substrate surface or to be incorporated into the substrate surface.        2. The reduction of occurrence of droplets through the use of higher-melting target materials increases the material costs and requires greater complexity in the operation of the arcing. The design of the arc sources becomes more complex in order to achieve the higher source currents and discharge voltages required for high-melting materials and the electric supplies likewise become more expensive.        3. Due to the generally greater chemical inertness of higher-melting materials, the desired chemical reactions of these high-melting materials with the components of the substrate surface usually only occur at higher temperatures (for example carbide formation).        4. The combination of the arc sources with electromagnetic and/or mechanical filters for droplet reduction results in a loss in ion current at the substrate. More importantly, the uniformity of such a treatment cannot be guaranteed over large substrate regions of the kind usually encountered in production systems.        5. In addition to the loss in ion current at the substrate, the use of filters also results in a reduction in the percentage of multicharged ions. These increase the probability of chemical (thermally stimulated) reactions since they strike the substrate with a correspondingly multiplied energy and therefore play an essential role in the formation of high-temperature stable bonds. It is in fact conceivable to compensate for the loss of multicharged ions by increasing the substrate bias, but it is generally advisable to avoid voltages greater than 1,000 V, not only to reduce arcing, but also for safety reasons.        6. Higher process gas pressure results in a droplet reduction, but also drastically reduces the substrate current and in turn primarily the percentage of multicharged metal ions. For reasons of process compatibility, it would, however, be desirable to also achieve sufficiently high substrate ion currents for the arc produced in the reactive gas.        
The disadvantages of the MIE based on the sputter method by means of HIPIMS can be summarized as follows:                1. No compatibility with arc layer deposition sources because the deposition rates are too low, i.e. it requires special sources and electrical supply for the operation of sputter sources.        2. The substrate ion current is only generated during the pulse.                    A large portion of the ions is captured by the magnetic field of the magnetron and does not reach the substrate, Muenz, W.-D. et al., Vacuum in Research and Practice, 19 (2007) 12.                        3. The operation of the sputter sources always requires a working gas that is incorporated into the substrate surface and results in mostly undesirable stress and instabilities in the substrate surface.        4. Working with reactive gas in sputter operation is difficult to control.        
Based on the above, the following conclusion can be drawn with regard to a use of MIE:
With the arc sources, the essential issue is the large droplets that cause problems because they do not have enough energy to permit them to diffuse further into the substrate after striking the substrate surface or to undergo chemical reactions with the components of the substrate surface. Otherwise, arc vaporization, with its potential for producing multicharged ions, would be best suited for performing the substrate pretreatment by means of metal ion etching.
Büschel, M. et al., Surf. Coat. Technol. 142-144 (2001) 665 have also disclosed the fact that arc vaporization sources can also be operated in a pulsed fashion in order to deposit layers. In this method, a continuous holding current is overlapped with a pulse current. It should also be noted in this context that the pulsing of the sources leads to a reduction of primarily large droplets in the layer deposition.
It is also known from the literature that pulsing cathodic arc sources without operating them continuously, i.e. continually reigniting them with each pulse, leads to a higher ion current that is primarily due to an increase in the percentage of multicharged ions, Oks, E. M. et al., Rev. Sci. Instrum. 77 (2006) 03B504.
The object of the invention is a zero layer deposition rate despite the fact that the arc deposition sources are operational, i.e. the production of an equilibrium state between material buildup and material removal on/from the surface, and the possibility of controlling this equilibrium state by means of the substrate bias. Another object of the present invention is to create a substrate pretreatment that is based on bombarding the substrate surface with ions, a significant percentage of which are metal ions and reactive gas ions and in the extreme case, it is possible to completely eliminate a working gas.
Another object of this invention is the diffusion of these ions into the substrate surface and a chemical reaction of these ions with components of the substrate surface.
Another object of this invention is the healing of substrate changes that were caused by preceding steps, e.g. cobalt depletion of the substrate surface due to wet chemical substrate cleaning.